The Long Term Evolution (LTE) wireless communication standard offers a high-capacity, high-speed wireless interface for use by mobile phones, data terminals, machine-type-communication (MTC) or machine-to-machine (M2M) equipment, and the like. However, in some instances it may be desirable to sacrifice aspects of an LTE terminal's performance, for example data capacity, in order to gain other benefits, such as reduced complexity and/or cost. The 3rd Generation Partnership Project has considered such possibilities, for example in connection with “low-cost” or “limited capability” User Equipment (UE), also referred to as a CAT-M UE.
The 3GPP (Third Generation Partnership Project) standards committees have recognized the need for LTE to support very large numbers of M2M UEs and have identified objectives for modifications to the existing LTE standards designed to support very large numbers of M2M UEs. Common requirements for such modifications are that they maintain compatibility with existing devices and limit the impact of M2M traffic on the high data rate and low latency requirements of current and future users.
It has be shown that time diversity can reduce transmission time by 35% when UEs are in deep coverage holes, for example UEs that are located indoors. This has been discussed in 3GPP TSG RAN WG1 Meeting #82, Aug. 24th-28th, 2015—R1-154489. However unless multiple Hybrid Automatic Repeat Request (HARQ) processes are supported, the UE transmission speed will be reduced. However, it is not obvious how the timing of the Downlink Control Information (DCI) for Uplink (UL) and Downlink (DL) grants can be sent and managed especially for Half-Duplex Frequency Division Duplexing (HD-FDD) UEs which cannot listen to the M-PDCCH (CAT M-Physical Downlink Control Channel) when transmitting.
It has been suggested to not use multiple HARQ processes (i.e. use only one process) in extreme coverage enhancement scenarios so the DCI timing becomes serial, for example DCI transmission followed by data transmission. The issue with this solution is that if time diversity is used the UE's data rate drops by a factor proportional to the number of HARQ processes supported. For example a UE's data rate can drop by a factor of 4 if 4 HARQ processes are supported. This drop in data rate can also negatively affect the UE's power consumption because of the amount of time required for transmission and reception.
Therefore there is a need for a method and system for transmitting control information for Category M User Equipment (UE) that is not subject to one or more limitations of the prior art.
This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.